U.S. authorities said on May 3 that a Russian man died over the weekend at a San Diego immigration detention center. The cause of death has not been determined.

U.S. Immigration and Customs Enforcement (ICE) said that 46-year-old Igor Zyazin had been in its custody since April 24. He had presented his Russian passport at San Diego's San Ysidro port of entry, bordering Mexico.

Officers found him unresponsive on May 1 at the Otay Mesa Detention Center. He was pronounced dead on his way to the hospital.

ICE says he was waiting for an interview with immigration officials to determine next steps in his case. He had been deported in 2009, and had no criminal history in the United States.

Russian diplomats have asked U.S. authorities for details on Zyazin's detention and death, TASS reported.

ICE says he is the sixth detainee to die in its custody since October. Its detention centers have about 30,000 beds.